Thermoplastic polyurethanes (TPU's) are well-known thermoplastic polymers, often elastomers, in particular for their very high tensile and tear strength, high flexibility at low temperatures, extremely good abrasion and scratch resistance. Thermoplastic polyurethanes are also known for their superior dynamic properties in particular very high rebound figures, low compression set and hysteresis loss. TPU's find application based upon their amenability to solution or melt processing into a versatile array of forms (for example films, tubes, complex molded shapes, coatings) via a broad range of techniques (for example extrusion, injection-molding, calendaring, solution coating).
A major technical challenge underlying thermoplastic polyurethanes is that although thermoplastic polyurethanes are relatively easy to process, the high temperature stability, durability, resistance to creep, (high temperature) dynamic behavior of these polyurethanes, as well as their stability in some commonly-used organic solvents, is less than might be desired for some applications.
Furthermore, following the trend compared with the reactive injection molded polyurethane, known as 2 liquid component polyurethane, there is a demand for lighter and better materials (preferably elastomeric), and even lower density polyurethane (PU) material which, in turn, represents an even bigger technical challenge to provide, if possible, equal or better physical and chemical properties compared to conventional low density TPU and PU (minimum of approximately 700 kg/m3) and certainly equal or better properties to ethylene-vinyl acetate (EVA) foams obtained by EVA foaming technology at density ranges between 0.1 and 0.4 g/cc.
In view of the above, there is a continuing need for a polyurethane formulator to find a polyurethane-forming composition/process that meets the above challenges.
Such compositions desirably would provide advantageous process capability, known in the market as thermoplastic process techniques such as extrusion, injection molding and thermo-cast, when the composition is in the thermoplastic state and advantageous elevated temperature stability and solvent resistance when the composition is thermoset during formation into the desired product in the mould. The concept of the present invention is to provide a TPU which is thermoplastically processable but which can subsequently be converted to a thermoset material by a cross-linking reaction.
There is also a need for post-crosslinkable films, mouldings, extruded profiles, and the like.
The present invention hence provides such desirable compositions, together with processes for the production of the compositions.
EP 305175 discloses a radiation curable composition for an adhesive including a polyurethane comprising residue of a polyether diol or a polyester diol and capped with residues of a hydroxyalkyl acrylate or methacrylate and non-polymerizable residues of a primary or secondary alcohol. This composition is liquid at room temperature, whereas the composition of the invention is an elastomeric solid at room temperature.
U.S. Pat. No. 6,444,721 describes a water dispersible radiation curable polyurethane composed essentially of aliphatic polyisocyanates, cycloaliphatic diols and/or diamines, compounds and at least one free-radically polymerizable unsaturated group.
U.S. Pat. No. 4,666,781 describes a linear thermoplastic polyurethane possessing acrylate side and terminal groups wherein the polyurethane is prepared by reacting poly- and/or diisocyanates with a mixture of (a) methacrylate- or acrylate-diols, (b) monoesters of methacrylic or acrylic acid and a diol and other organic polydiol compounds. This polyurethane composition is used as a binder in the magnetic layer of a magnetic material in magnetic tape and was conceived so as to allow the distribution of the magnetic pigment in the binder (a relatively flexible binder is needed).
U.S. Pat. No. 4,762,884 describes a process for the production of polyurethanes using cross-linking agents.
U.S. Pat. No. 4,560,456 describes magnetic recording media which partially comprise polyurethane acrylates having number average molecular weights between 1,800 and 10,000 in addition to acrylate prepolymers, monomeric acrylates and N-vinyl monomers. These compositions deliver radiation-curable coatings suitable for use in magnetic recording media but do not deliver materials suitable for melt processing into articles such as those provided in the current invention.
U.S. Pat. No. 4,507,458 describes radiation curable urethaneacrylate resins suitable for solution processing and use as thermally or radiation-curable adhesives or coatings. However, this process does not deliver materials suitable for melt processing into high quality articles such as those provided in the current invention.
U.S. Pat. No. 4,133,723 describes energy-curable coating compositions based upon unsaturated urethane resins but these lack a chain extender and consequently do not have a mesophase structure. None of the documents cited above teaches or suggests the present invention.